The present invention relates to a display device capable of preventing its image retention.
As an image display device for displaying images by making use of the light emission of the phosphor, there is the conventional TV receiver using the cathode ray tube (CRT). In addition to this, there is also a thin flat-type image display device which has been available in recent years, that is, the plasma display panel display device (abbreviated to PDP display device, hereinafter) using the plasma display panel (abbreviated to PDP, hereinafter), which utilizes the light emission of the phosphor excited by the ultra-violet ray in each of the discharge cells, the light emission inducted by the electric discharge of inert gases such as Ne (Neon) and Xe (Xenon), with setting each of the discharge cells arranged in the matrix manner as the unit region. The PDP display device is suitable for a large-sized displaying, and its market has been expanding. Note that the panel structure, the electric discharge mechanism, and the display method of the AC-type PDP are disclosed in, for example, JP-A-10-319901 corresponding to U.S. Pat. No. 6,020,687.
Furthermore, as the thin flat-type image display device utilizing the light emission of the excited phosphor, there is also the FED (Field Emission Display), which utilizes the light emission of the excited phosphor induced by irradiating the electron beam to the phosphor from the electron source in which a large number of electron emitting elements are arranged in a matrix manner (two dimensionally).
Meanwhile, not only the PDP display device but also all image display devices utilizing the light emission of the phosphor has the problem as follows. That is, if the static image with high luminance level is displayed for a long time, the phosphor is degraded, and as a result, the difference in luminance is caused between that part and the other part, that is, a so-called image retention occurs.
For the prevention of the image retention, there is the method as described in JP-A-5-344371, in which, when the displayed image remains unchanged for a predetermined amount of time or more, the image is regarded as a static image, and the luminance level of the entire screen is lowered. In addition, as described in JP-A-2000-227775, there is also the method that when a static image is displayed on the screen for a predetermined amount of time or more, the entire screen is moved by several dots to an almost imperceptible extent.
Furthermore, in the case where both the moving image and the static image are present on the image, there is the method as described in JP-A-2002-351442, in which the static image part is distinguished from the entire screen, and when the static image part remains unchanged for a predetermined amount of time or more, the luminance level only in the static image part is lowered.